FIG. 1 diagrammatically illustrates a typical configuration of a guided acoustic travelling wave lens device--one that employs a relatively narrowly dimensioned traveling wave channel--as comprising a laser 10, the optical beam output 11 of which is focussed by a cylindrical lens arrangement 12 and deflected by a mirror 13 onto an acousto-optic beam deflector 14, to which an RF input signal is applied. The acousto-optically modulated beam is then re-imaged by a further spherical-cylindrical lens arrangement 15 onto a traveling lens cell 16, than contains a traveling wave lens transport medium 17 and a traveling wave lens launching transducer 18. The scanned beam is then imaged onto an image collection medium, such as a photographic film 19.
For a non-limiting illustration of examples of documentation describing such guided acoustic traveling wave lens; devices, attention may be directed to an article entitled: "Optical Beam Deflection Using Acoustic-Traveling-Wave Technology," by R. H. Johnson et al, presented at the SPIE Symposium On Optical, Electro-Optical, Laser and Photographic Technology, August 1976, FIG. 6 of which corresponds to FIG. 1, above, an article entitled: "Guided acoustic traveling wave lens for high-speed optical scanners," by S. K. Yao et al, Applied Optics, Vol. 18, pp 446-453, Feb. 1979, and the U.S. Pat. No. 3,676,592 to Foster.
In such guided wave devices the properties of the fluid will affect the characteristics of the acoustic wave lens traveling through it. In particular, since fluid velocity and friction force are functions of distance from the transducer, the acoustic power P and frictional power loss Pf are also functions of distance. Due to the viscous properties of liquid, particularly in the vicinity of its interface with the boundaries of the channel, external forces iLmparted by the electro-acoustic transducer do not maintain a constant acoustic power density of the acoustic wave over the length of the cell. For a rectangular waveguide having a constant narrow cross-section of width w and height h (where h&lt;&lt;w), it has been demonstrated that acoustic power density will undesirably undergo an exponential attenuation along the length x of the waveguide.